Uses of Herbicides
A herbicide is a compound which controls or modifies plant growth, e.g., killing, retarding, defoliating, desiccating, regulating, stunting, tillering, stimulating, dwarfing and the like. "Plant" refers to all physical parts, including seeds, seedlings, saplings, roots, tubers, stems, stalks, foliage and fruits. "Plant growth" is meant to include all phases of development from seed germination to natural or induced cessation of life.
Herbicides are generally used to control or eradicate weed pests. They have gained a high degree of commercial success because it has been shown that such control can increase crop yield and reduce harvesting costs.
Herbicidal effectiveness is dependent upon several variables. One of these is the time or growth related method of application. The most popular methods of application include: pre-plant incorporation into the soil; pre-emergence surface treatment of seeded soil; and post-emergence treatment of the plant and soil.
The most important determinant of herbicidal effectiveness is the susceptibility of the beneficial crop and selectivity toward weeds. Certain herbicidal compounds are phytotoxic to some weed species but not to others.
A manufacturer of a herbicide generally recommends a range of rates and concentrations calculated to maximize weed control. The range of rates usually varies from approximately 0.1 to approximately 50 pounds per acre (lb/A) [0.112 to 58 kilograms per hectare (k/ha)], usually from 0.1 to 25 lb/A (0.112 to 26 k/ha). The actual amount used depends upon several considerations, including, crop tolerance, particular weed susceptibility and overall cost limitations.
Some herbicides display exclusive selectivity toward weed species. Many are toxic to both weeds and the intended crop beneficiary. Therefore, a particular herbicide may proscribe its injurious effect on the cultivated crop even though it may otherwise provide excellent control of weeds found in the crop field.
To preserve the beneficial aspects of herbicide use and to mitigate crop damage, many herbicidal antidotes have been prepared. These antidotes reduce or eliminate damage to the crop without substantially impairing the beneficial effect of the herbicide. For example, see U.S. Pat. Nos. 4,021,224 and 4,021,229 and Belgian Pat. No. 846,894.
Although several explanatory theories have been advanced, the precise mechanism by which an antidote reduces herbicidal crop injury while retaining week injury has not been conclusively established. An antidote compound may in fact be a remedy, interferent, protectant, or antagonist. As used herein, "antidote" describes, i.e., the continued effect of establishing herbicidal selectivity of herbicidal phytotoxicity to weed species and reduced or nonphytotoxicity to cultivated crop species.
As an alternative mode of action, the compounds of this invention may interfere with the normal herbicidal action of the thiolcarbamate-type herbicides to render them selective in their action. Whichever mode of action is present, the corresponding beneficial and desirable effect is the continued herbicidal effect of the thiolcarbamate with the accompanying decreased herbicidal effect on desired crop species. This advantage and utility will become more apparent hereinafter.
Therefore, the terms "herbicide antidotes" or "antidotal amount" is meant to describe that effect or the amount which produces the effect which tends to counteract the normal injurious herbicidal response that the herbicide might otherwise produce. Whether it is to be termed a remedy, interferent, protectant, or the like, will depend upon the exact mode of action. The mode of action is varied, but the effect, which is desirable, is the result of the method of treating the soil in which a crop is planted.
Thiolcarbamate herbicides are particularly effective in the control of grassy type weeds which interfere with the cultivation of a wide variety of crops, e.g., barley, corn, lentils, peanuts, peas, potatoes, soybeans, spinach, tobacco and tomatoes. Frequently, the beneficial use of the thiolcarbamate can be enhanced by the addition of an antidote compound.